Mirror coating

ABSTRACT

A mirror coating which possesses properties which are advantageous for the construction of a mirror assembly. The mirror coating has a complex reflective index which is wavelength dependent, and wherein the real component is dominant and the imaginary component is negligible within a predetermined spectral band pass region, and the imaginary component is substantially within a spectral region other than the predetermined spectral band pass region, and wherein the mirror coating exhibits substantially neutral reflected chromaticity as observed with reflected ambient light.

FIELD OF THE INVENTION

The present invention relates to a mirror coating and more specifically,to a mirror coating which provides improved performance characteristicsrelative to a mirror assembly which includes a subassembly which mayemit, or receive, electromagnetic radiation in predetermined spectralbands which may be visible, or invisible.

DESCRIPTION OF THE PRIOR ART

The beneficial effects of employing auxiliary or so called third brakelamps [center high mounted stop lamps] has been known for some time.Further, the inventor hereof has disclosed improved mirror assemblieswhich augment center high mounted stop lamps [CHMSL] and which provideadditional laudatory benefits. These mirror assemblies are disclosed inU.S. Pat. Nos. 5,014,167 and 5,207,492, both of which are incorporatedby reference herein.

The mirror assemblies disclosed in the above-captioned patents utilizedichroic mirrors which are operable to reflect a broad band ofelectromagnetic radiation within the visible light portion of thespectrum while simultaneously permitting electromagnetic radiationhaving wavelengths which reside within a predetermined narrow spectralband, (sometimes referred to as in-band radiation) to pass therethrough.In this fashion, the dichroic mirror remains an excellent visual imagereflector, that is, achieving luminous reflectance which is acceptablefor automotive applications, for example, while simultaneously achievingan average transmittance in the predetermined spectral band of at least58%. When the predetermined band pass region is relatively narrow, thatis, such as 30 nanometers or less, average in-band transmittance of 80%or more can be achieved, with peak transmittance in excess of 95% beingcommon.

As disclosed in the previous patents, selective spectral bands ofvisible light or invisible electromagnetic radiation can be utilized forvarious applications. Spectral bands corresponding to the visible colorsred, blue, green, and yellow as well as non-visible spectral bands suchas infra-red, ultraviolet or microwave may be selected for applicationswhich include providing visual signals or displays to an operator of thevehicle, or to those in adjacent vehicles, or in the alternative,providing an environment where active or passive sensors of assortedconstruction may be placed in an advantageous, concealed location behinda corresponding mirror surface such that the sensors may achieve variousadvantageous functions.

While the mirror assemblies disclosed in the above-identified patentshave operated with a great deal of success, certain inherent physicalfeatures or characteristics of the earlier disclosed mirror assembliesutilizing dichroic mirrors have detracted from their aestheticacceptability in certain environments. More specifically, and dependingupon the band of electromagnetic radiation which is emitted, orreceived, by the mirror assembly, the reflective surface of thesedichroic mirrors, as viewed in natural light, may appear to have variouscolors, or tints which, while not detracting from their usefulness, maynot be entirely aesthetically appealing in all automotive applications.For instance, when mirror assemblies are employed which are operable toemit visible light which is in the spectral band which includes thecolor red, the dichroic mirrors employed with same can appear, undernormal ambient lighting conditions, to have a slight blue color or tint.Further, and when these same mirror assemblies are viewed under ambientlighting conditions, it is possible, under some circumstances, as forexample, in extremely bright sunlight, to see the outline of theunderlying sensors or light emitting assemblies upon close examination.

Another perceived limitation in these same dichroic mirrors relates tothe ability of the dichroic mirrors to pass certain wavelengths of lightother than the predetermined narrow spectral band pass selected which,over a prolonged period of time, may have deleterious consequences forthe subassemblies of the mirror assembly which may be bonded or fastenedtogether using various polymeric based adhesives. More specifically,adhesive compositions using various polymeric based substances maydegrade when exposed for prolonged periods of time to ultraviolet lightto such a point that the adhesive bonds weaken and fail. Consequently,the inventor has continued to investigate various improved mirrorcoatings which can be used in the aforementioned mirror assembly, andwhich will, to a much greater extent, substantially conceal theunderlying sensors or light emitting subassemblies, provide asubstantially neutral chromatic appearance, and simultaneously absorbwavelengths of electromagnetic radiation which may otherwise betransmitted into the mirror assembly and which, over time, will degradeor otherwise be harmful to the subassemblies concealed by the mirror.

Other previous coatings such as that disclosed in U.S. Pat. No.5,200,855 to Meredith et al. have been found to be substantiallyinadequate in satisfying the new aesthetic and operational requirementsdiscussed, above. In this regard, the patent to Meredith et al.discloses a mirror coating which has a periodic, layered structure.While this periodic structure provides several advantages, for example,it provides for ease of computation with respect to the calculation ofthe optical requirements of the coating, it does not, however, yieldcoating performances which meet the operational parameters disclosedabove. For example, these periodic stacks, which are expressed as [H LH]^(n), wherein N equals 2 or 3 are primarily useful in producing highpurity, red or orange transmission filters. These filters, however, havesevere limitations in that moderately high, neutrally chromaticreflectance, high in-band transmittance and substantial out-of-bandabsorbance are not substantially achievable simultaneously with such acoating.

In the present invention, however, the inventor has departed from theteachings of the prior art and has provided a mirror coating which has anon-periodic stack of materials, whose layers have irregularthicknesses, and where one of the materials has a wavelength dependent,complex refractive index. Accordingly, an optimized coating isachievable which readily satisfies the various characteristics discussedabove, that is, the mirror has an acceptable luminous reflectance, hassubstantially neutral chromaticity when viewed with ambient naturallight, has high in-band transmittance, and further has moderateout-of-band absorbance.

Therefore, the present invention, when applied to a transparent ortranslucent substrate, creates a mirror which may be utilized in amirror assembly, as disclosed in the prior art, and which furtherprovides a means for enclosing an emitter, or receiver ofelectromagnetic radiation which are individually operable to providevarious signals to the operator of an overland vehicle, adjoiningobservers, or nearby electromagnetic receivers or sensors; and whichfurther substantially conceals the underlying emitters or receivers,while simultaneously providing a neutrally reflective appearance whenviewed under ambient lighting conditions, and further being an excellentreflector of ambient light in the form of reflected perceivable images,and an excellent transmitter of the predetermined bands ofelectromagnetic radiation which are emitted or received by thesubassemblies which are concealed by the mirror.

OBJECTS AND SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide animproved mirror coating.

Another object of the present invention is to provide a mirror coatingwhich may be utilized with a mirror assembly, and wherein the mirrorassembly may be manufactured and installed as original equipment on anoverland vehicle and the like, or which may further be manufactured inthe manner of a retrofit.

Another object of the present invention is to provide a mirror coatingwhich may be utilized with a mirror assembly, and wherein the mirror,and mirror coating, may be readily installed or integrated with othermirror technology such as motorized actuators, heater elements and filmsof various types including electrochromic dimming films.

Another object of the present invention is to provide a mirror coatingcontaining one or more layered materials having a complex refractiveindex which is wavelength dependent, and wherein the real component ofthe refractive index is dominant and the imaginary component isnegligible within a predetermined spectral band pass region, and furtherthe imaginary component is substantial within a selected spectral regionother than the predetermined band pass region.

Another object of the present invention is to provide a mirror coatingwhich exhibits substantially neutral reflected chromaticity as observedwith reflected ambient light, has a peak transmission of not less than60% within a selected spectral band pass region, and a peak absorbanceof not less than 30% within a spectral region other than thepredetermined spectral band pass region, while simultaneouslymaintaining greater than 50% luminous reflectance.

Another object of the present invention is to provide a mirror coatingwhich is operable to impede the penetration of predetermined wavelengthsof light other than those in the predetermined spectral band passregion, thereby further obscuring or otherwise making indiscernible thesensors or other light emitting or receiving subassemblies positionedbehind the mirror, under various ambient lighting conditions, oralteratively, protecting the sensors or emitters or other internalassemblies from undesired excessive exposure to deleterious out-of-bandradiation.

Another object of the present invention is to provide a mirror coatingwhich provides substantially neutral reflected chromaticity over a broadrange of angles of incidence, [AOI] while simultaneously providinggreater than 50% luminous reflectance.

Another object of the present invention is to provide a mirror coatingwhich includes a non-periodic series or stack of materials havingirregular thicknesses, and which are operable to provide an optimizedcombination of the characteristics noted above.

Another object of the present invention is to provide a mirror coatingwhich is operable to obtain the individual benefits to be derived fromrelated prior art assemblies and compositions, while avoiding thedetriments individually associated therewith.

Further objects and advantages are to provide improved elements andarrangements thereof in a mirror coating, and related mirror assembly,for the purposes intended, and which is dependable, economical, durable,and fully effective in accomplishing these intended purposes.

These and other objects and advantages are achieved in a mirror coating,and wherein the mirror coating includes a non-periodic stack orsuccession of materials in a layered interference filter structure, andwherein the mirror coating exhibits substantially neutral reflectedchromaticity as observed with reflected ambient light; has a peaktransmittance not less than 60% within a predetermined spectral bandpass region; has a peak absorbance not less than 30% within a regionother than the predetermined spectral band pass region, whilesimultaneously achieving a luminous reflectance of greater than 50% forthe ambient light striking the mirror coating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective environmental view of a mirror assemblyutilizing the mirror coating of the present invention.

FIG. 2 is a partial, exploded, perspective view of a portion of themirror assembly which utilizes the mirror coating of the presentinvention.

FIG. 3 is a partial, exploded, perspective view of a portion of themirror assembly which utilizes the mirror coating of the presentinvention.

FIG. 4 is a top plan view of the electronic circuit board shown in FIG.2 with the hexagonal reflectors removed.

FIG. 5 is a bottom plan view of the circuit board shown in FIG. 4.

FIG. 6 is a graphic illustration of reflectance, transmittance, andabsorbance as compared with wavelength for a first form of the mirrorcoating composition of the present invention, along with a graphicillustration of an emitter or receiver response.

FIG. 7 is a graphic illustration of reflectance, transmittance andabsorbance as compared with wavelength for a second form of the mirrorcoating composition of the present invention along with a graphicillustration of an emitter or receiver response.

FIG. 8 is a graphic illustration of reflectance, transmittance andabsorbance as compared with wavelength for a third form of the mirrorcoating composition of the present invention along with a graphicillustration of an emitter or receiver response.

FIG. 9 is a graphic illustration of reflectance, transmittance andabsorbance as compared with wavelength for a fourth form of the mirrorcoating composition of the present invention along with a graphicillustration of an emitter or receiver response.

FIG. 10 is a graphic illustration of reflectance, transmittance andabsorbance as compared to wavelength for a fifth form of the mirrorcoating composition of the present invention along with a graphicillustration of an emitter or receiver response.

FIG. 11 is a greatly enlarged, graphic, vertical sectional view of thesecond form of the mirror coating composition of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring more particularly to the drawings, the mirror coating, in itsvarious forms, finds usefulness when utilized in combination with amirror assembly 10 which is best illustrated in the perspective view ofFIG. 1, and the exploded views which are shown in FIGS. 2 and 3,respectively. Further, FIG. 11 provides a graphic depiction of thesecond form of the present mirror coating and illustrates thenon-periodic, stacked arrangement of the materials. The various forms ofthe present invention will be discussed in greater detail hereinafter.

For convenience sake, the mirror assembly which is shown and describedherein is illustrated as it would be configured if it were installed onan overland vehicle (not shown) and which is of conventional design, andwherein the mirror assembly may be mounted on the vehicle in place ofthe rearview mirror which is normally located in the passengercompartment or, as shown in FIG. 1, in place of the sideview mirrorswhich are mounted on the exterior surface 11 of the overland vehicle. Asbest seen by reference to FIGS. 1 and 2, the mirror assembly 10 ismounted on the exterior surface 11 of the overland vehicle by means of ahousing 20 which includes a substantially continuous rear wall 21, and aside wall 22 which extends generally normally, and substantiallyforwardly relative thereto. It should be understood that the wordforward when referring to the mirror assembly means the mirror assemblyis oriented in a fashion which permits viewing rearwardly of theoverland vehicle when an operator is seated in the passenger compartmentof the overland vehicle. The side wall 22 defines an aperture 23 ofpredetermined dimensions.

The housing 20 is operable to enclose all manner of assemblies, devices,and/or sensors which may individually operate as a receiver, emitter, ortransceiver of electromagnetic radiation 30. These receiver(s) oremitter(s) operate to produce or receive wavelengths of electromagneticradiation which are substantially matched to the peak wavelengthtransmittance characteristics of a mirror which is borne by theenclosure or housing and disposed in substantially occluding relationrelative to the aperture 23. The mirror and its characteristics as wellas the coating composition utilized with same will be discussed ingreater detail hereinafter. For purposes of this invention, however, itshould be understood that the terms "transmit" or "transmittance" shallmean the passage of electromagnetic radiation, regardless of direction,through the associated mirror. Further, the terms "pass" or "passage"shall also describe the same phenomena. Additionally, the phrase"interference filter" means a filter that controls the spectralcomposition of transmitted energy partially by the effects ofinterference. In this regard, these filters are made up of thin layersof conductive, semi-conductive, or dielectric materials which act, incombination, to produce a filter which has high transmission in narrowspectral bands. In the present form of the invention as shown in FIG. 1,the receiver(s) and/or emitter(s) of electromagnetic radiation 30 emitand/or receive light having wavelengths which include the 630 through680 nanometer band, and which physically manifests itself as theperceived color red. The invention, however, is not limited to the peakwavelengths recited herein, but may further be used with any chosenwavelength band such that any visual spectrum color can be seen, or anyinvisible spectral band may be emitted, or received. Further, thepresent invention could also include more than one or a combination ofsources or receivers of electromagnetic radiation.

The receiver(s) and/or emitter(s) of electromagnetic radiation 30 aredepicted herein as including a modular LED [Light Emitting Diode] arrayor bank of LEDs 31 which are individually mounted on a circuit board 32,and which are operable to produce visible light having the wavelengthswhich include the 630 through 680 nanometer band. Additionally, a photodetector 31A is depicted in FIGS. 2 and 4 and which is operable toreceive electromagnetic radiation [visible and invisible] which ispassed by the mirror coating and which produces a corresponding controlsignal. This control signal provides an input to the control circuitelements 31B which adjusts the power output and thus the correspondingbrightness, in the present example, of the individual LEDs.

It should be understood that individual LEDs 32A may be manufacturedwhich produce other wavelengths or perceivable colors, such as amber,green, or infrared, however, in such a case, the mirror employed withsame would either include specific areas whose individual transmissioncharacteristics would be substantially matched to the spectral bands oflight which are emitted by the LEDs which are immediately adjacentthereto, or in the alternative, would be operable to pass the selectedspectral bands of electromagnetic radiation which are emitted orreceived by the assemblies enclosed within the housing 20. Acommercially available LED which fits these performance parameters orcharacteristics, as illustrated in FIG. 2, is manufactured by HewlettPackard of San Jose, Calif. under the trade designation HPWR-A300. Thecommercially available LED, which is noted above, has high efficiency,and is an ultra-radiant red LED having a peak wavelength which fallssubstantially within the 630-680 nanometer band. It should beunderstood, that each of the respective LEDs has a transmission pathwhich is substantially oriented in a direction which is generallyperpendicular to the circuit board 40. Suitable electrical leads 33electrically connect the bank of LEDs 31 with the braking, ordirectional signalling assemblies [not shown], as well as a source ofpower which is borne by the overland vehicle.

The receiver and/or emitter of electromagnetic radiation 30 includes, asearlier discussed, a circuit board 40 which has a top or forwardlyfacing surface 41, and a back, or rearwardly facing surface 42. Thecircuit board further has a peripheral edge 43 which is shaped in apredetermined fashion such that the circuit board may mate, or otherwisenest within the housing 20. FIGS. 2 and 4 illustrate views of the topplan, or forwardly facing surface of the circuit board. It should beunderstood that the circuit board may be utilized on the left, and rightside, respectively of the overland vehicle [not shown]. The electricalleads as shown in FIG. 2 are oriented on the right side of the circuitboard and facilitate wire routing to the braking, directional signallingassembly, power supply and other control circuitry of the overlandvehicle [not shown]. FIG. 5 shows the bottom plan view of the samecircuit board. It is to be understood that a circuit board which is usedon the passenger side of the vehicle (as seen in FIG. 4) issubstantially a mirror image of that used on the driver's side and whichis depicted in FIG. 2. In this regard, the electrical leads 33 which areillustrated in FIGS. 4 and 5, respectively, are oriented on the leftside, as viewed in FIG. 4, of the circuit board and facilitate wirerouting to the braking, directional signalling assembly, power supplyand other control circuitry of the same overland vehicle [not shown].

Referring more particularly now to FIG. 4, the array or bank of LEDs 31is generally mounted on the top or forwardly facing surface 41 of thecircuit board 40 and disposed in a generally hexagonal and matrix-likepattern. As will be discussed in greater detail, hereinafter, anddepending upon the signal desired to be transmitted to a person orlocation positioned outside of the overland vehicle, it may be possibleto energize all of the LEDs 31, and have them remain energized torepresent a specific signal; or alternatively, it is possible toenergize a subset, or smaller number of the bank LEDs and have themflash in a predetermined pattern to represent other possible signalssuch as a left or right turn signal; braking; or possibly a signalindicating that the overland vehicle is backing up, as by the use of arapidly intermittent or strobe light flashing pattern. It should beunderstood, therefore, that the array of LEDS constitutes asemi-reconfigurable matrix display whose apparent outline is determinedby the circuit board, and whose relative brightness changessubstantially in concert with the ambient lighting levels sensed by thephoto detector 31A as discussed above.

As best seen in FIG. 2, substantially hexagonal reflectors 44 areoperable to matingly engage the circuit board 40 at predeterminedlocations by means of a pair of pins which are generally indicated bythe numeral 45. It should be understood that the hexagonal reflectorsinclude an internal boundary 50 which has a highly reflective surfaceapplied thereto as by means of vacuum metalization or similar techniqueswhich are well known in the art. The individual reflectors 44 areoperable to reflect electromagnetic energy from the emitter outwardlyfrom the circuit board. The individual reflectors 44 may bemanufactured, in the alternative, as a single reflector havingindividually discreet reflector cups which are substantially similar tothe single reflectors illustrated. Of course, when the single reflectoris employed, the individual pins are not required, rather only a fewpins are necessary and are positioned around the perimeter of thereflector to orient and secure the single reflector in a proper positionon the circuit board. As best seen by reference to FIG. 3, andpositioned immediately forward of the circuit board 40, and thehexagonal reflector 44, is an array of convexo-convex lenses 60. As bestseen by reference to FIG. 3, the array of convexo-convex lenses 60 areformed in a single transparent plastic piece 61. In the single piece 61there is provided a single, convexo-convex lens which is disposed inregistration with each of the individual reflectors 44. Theconvexo-convex lens array is configured, or otherwise arranged, suchthat the center of each of the respective lenses are disposed insubstantial alignment with the beam center for each of the respectiveLEDs 32. The lens array further serves to collimate the light emittingfrom the respective LEDs, and which has been reflected in a forwarddirection by the reflector 44 and further to magnify the apparent LEDluminous area, that is, the area of luminosity which can be readilydiscerned by the human eye.

A baffle assembly 70 is positioned intermediate the mirror and thereceiver or transmitter of electromagnetic radiation 30. The baffleassembly of the preferred embodiment includes a polymeric based lightcontrol film which permits ambient, or artificial light generated by theelectromagnetic emitter to escape from the housing 20. The light controlfilm, a variety of which is manufactured by 3M Company under the tradedesignation LCFS ABRΦ35 OB 48 CLR GLS 0.025" is a thin plastic filmenclosing a plurality of closely spaced, black colored microlouvers. Thelight control film is approximately 0.025 inches [0.75 millimeters]thick, and the microlouvers are spaced approximately 0.005 inches apart[0.127 millimeters]. The microlouvers may be a transparent black, or anopaque black, and further, the microlouvers may be positioned in variousangular positions and at various spacings to provide a viewing angle, asin the case of visible light, which may include angles as narrow as 48degrees plus or minus 6 degrees, or as wide as 90 degrees plus or minus15 degrees. It should be understood that the baffle assembly permitslight emitted by the electromagnetic radiation source 30 to escapewithin a predetermined viewing angle from the housing 20, and travelrearwardly and outwardly relative to the overland vehicle, not shown.Further, the baffle assembly is operable to inhibit, or block, the lightemitted by the electromagnetic emitter 30 from travelling outside thepredetermined viewing angle and into the view of the operator of theoverland vehicle [not shown]. In the preferred embodiment, the baffleassembly is laminated or otherwise attached or made integral with therearward facing surface of the mirror by means of various adhesivevehicles which are well known in the art. As earlier indicated, themirror will be discussed in greater detail hereinafter.

The mirror assembly 10 further includes first and second fresnel prismsheets 80 and 90, respectively. Each of the fresnel prism sheetsutilized is positioned intermediate the receiver or emitter ofelectromagnetic radiation 30, and the baffle assembly 70. Each prismsheet serves to bend or otherwise redirect the collimated light which ispassed through the array of convexo-convex lenses 60. The light is bentby the prism sheets towards the predetermined viewing angle establishedby the baffle assembly 70 to minimize light loss, or in other words, insuch a fashion as to align the axis of the peak beam intensity of theindividual LEDs 32 with the peak transmission axis of the baffleassembly. The individual fresnel prism sheets may also be used todeflect the light upwardly or downwardly relative to the position of themirror assembly 10 as it is mounted on the overland vehicle [not shown].This deflection or directional orientation of the emitted lightupwardly, or downwardly, is achieved by rotation of the individualfresnel prism sheets within a plane which is substantially parallel tothe mirror, prior to assembly of the mirror assembly 10. This deflectionor directional orientation of light is useful in compensating for heightdifferences, relative to the surface of the earth, which may existbetween the mirror assembly 10, as mounted on a predetermined overlandvehicle, and for example, observers seated in vehicles in a adjoiningtraffic lane. Therefore, the individual fresnel prism sheets areselected in such a fashion so as to cause the electromagnetic radiationwhich is received or emitted by the mirror assembly 10 to be directedalong a predetermined path appropriate for the specific vehicle platformupon which it is employed. In an alternative design, the individualprism sheets may be replaced by a deviator sheet (not shown) which maybe of a fresnel, refractive design, or in the alternative a hybrid,refraction/total internal reflection [TIR] type design.

A black mask comprised of a substantially opaque paint or other similarcoating or substance 100, is typically applied to the mirror in areasnot covered by the baffle assembly and thereby outlines the area throughwhich light or other electromagnetic radiation passes. This mask isapplied normally to the rearward surface of the mirror. The mirror willbe discussed in the paragraphs which follow. It should be understood,however, that in certain circumstances, and wherein the combinedluminous reflectance and absorbance of the mirror coating exceedapproximately 85%, this mask may be omitted.

As best seen by reference to FIGS. 1 and 3, the mirror assembly 10 ofthe present invention includes a semi-transparent mirror 110 whichselectively passes, and reflects electromagnetic radiation havingpredetermined wavelengths. As explained earlier, the receiver and/oremitter of electromagnetic radiation 30 is operable to produce orreceive electromagnetic radiation having the wavelength characteristicwhich include the spectral band of electromagnetic radiation which ispassed or otherwise transmitted by the mirror 110. In the examplesprovided hereinafter, the mirror 110 is operable to transmit thespectral band which includes 630-680 nanometers, and which correspondswith the perceived visible spectrum color red. Of course, should adifferent visible color or non-visible spectral band be desired, then,in that event, a different mirror would be selected which wouldpreferentially transmit or pass the selected wavelength corresponding tothe spectral band selected. It should be understood that the mirror 110is operable to transmit or pass wavelengths which predominantly fallwithin the predetermined spectral band selected and which is normallynot greater 100 nanometers in width for an ultraviolet or visiblespectral band; 300 nanometers for an infrared band; and 2 to 3millimeters for a radio, or microwave band.

As best seen in the drawings, the mirror 110 has a forwardly facingsurface, and a rearwardly facing surface upon which the opaque mask 100is applied. As earlier discussed, it should be understood that the word"forward," when referring to the mirror assembly 10, means that themirror assembly is positioned or otherwise oriented such that anoperator may view rearwardly of the vehicle [not shown] when theoperator is seated in the passenger compartment of the overland vehicle.In this regard, the mask 100 is operable to substantially inhibit anylight leakage from the electromagnetic emitter 30 which is positionedinternally of the housing 20, and thereby outlines a graphic shape ofthe emitter array. Further, the opaque mask prohibits excessive ambientlight from entering the mirror assembly 10 through any mirror surfaceextending beyond the peripheral edge of the baffle assembly 70.

In order to accomplish the foregoing objectives, the mirror 110 of thepresent invention includes a mirror coating having a non-periodicsuccession or stack of materials in a layered interference filterstructure. The mirror coating, as noted above, has one or more layeredmaterials which have a complex refractive index which is wavelengthdependent, and wherein the real component is dominant, and the imaginarycomponent is negligible within a predetermined band pass region.Additionally, the imaginary component is substantial within a spectralregion other than the predetermined band pass region. More specifically,the refractive index of this material may be represented by theexpression [n+ik].sub.λ wherein n represents the real component of therefractive index, and the ik represents the imaginary component each fora given wavelength λ. For the present invention, materials are selectedwherein the real component ranges from approximately 1.5 to 4 dependingon the wavelength and materials selected, and wherein k ranges from 2.5to 0 depending on the specific materials and wavelength selected. Inthis formula, i is the unit vector in the imaginary axis, and k is thecoefficient known as the extinction coefficient and which is related tothe absorption coefficient and which is known by the relationship:##EQU1##

In this regard, the mirror coating imparts to the mirror 110substantially neutral reflected chromaticity as measured using a whitereflected source such as CIE - Illumination C, D65, E or B; has a peaktransmittance not less than 60% within the predetermined band passregion; has peak absorbance not less than 30% within regions other thanthe predetermined spectral band pass region; and which simultaneouslyhas a luminous reflectance greater than 50% of the ambient lightstriking the mirror coating.

Examples of the mirror coating compositions which may be applied toeither the forward or rearwardly disposed surfaces of mirror 110 byconventional deposition techniques, are set forth below. In each of theexamples provided, the non-periodic stack of materials are referred toas a first layer, second layer, etc. In each of these instances, itshould be understood that the first layer of material is appliedimmediately to the forward or rearward facing surface of the mirror 110.Subsequent layers, that is, the second layer, is applied immediately tothe top surface of the first layer, and the third layer is applied tothe top surface of the second layer. Examples of the several forms ofthe mirror coating are set forth below:

EXAMPLE 1

The mirror coating composition, as described above, includes a coatingwhich has a non-periodic stack of materials and which includes: a firstlayer of copper having a thickness dimension of about 3.68 nanometers; asecond layer of silicon dioxide having a thickness dimension of about87.68 nanometers; a third layer of titanium oxide having a thicknessdimension of about 63.70 nanometers; a fourth layer of silicon dioxidehaving a thickness dimension of about 77.68 nanometers; a fifth layer oftitanium oxide having a thickness dimension of about 42.28 nanometers; asixth layer of silicon dioxide having a thickness dimension of about81.21 nanometers; and a seventh layer of titanium oxide having athickness dimension of about 61.83 nanometers.

The mirror coating composition, above, is best understood by a study ofFIG. 7, and wherein the composition is shown with respect to itspercentage reflectance, transmittance and absorbance as compared withwavelength in nanometers. Further, the emitter output, or receiverresponse is illustrated in relative comparison to the other indicia. Asshown therein, the mirror coating of the present composition achieves aluminous reflectance of approximately 53.29% at approximately a 30degree angle of incidence [AOI]. Further, the reflective properties ofthis mirror coating are substantially neutral, that is, it has a 1931CIE x and y color coordinates of 0.3099 and 0.3608, respectively, whenilluminated by white light. It being understood that a perfectly neutralmirror has 1931 CIE x and y color coordinates of 0.3333 and 0.3333,respectively. Further, the same mirror coating composition has a peaktransmittance of approximately 81.2% at the in-band frequency of 680nanometers, and a peak, out of band absorbance of 36.02% at a frequencyof 480 nanometers.

It should be understood, that the thickness dimension of each of thelayers discussed above may be varied by as much 2% without irreparablyaltering its performance characteristics. Similarly, for each of thecoating compositions discussed above, adjustments may be made forstoichiometric variations in the materials which are actually depositedor made integral with the individual layers. For example, the oxidationstate has an impact on the refractive index coefficients. Therefore,different deposition techniques may result in slightly different layerdensity and oxidation levels with a corresponding change, or shift inthe refractive index. However, one skilled in the art will be able tocompensate for this change or shift by varying the thickness of theindividual layers in a way to compensate for these stoichiometricvariations.

It should be further understood, that this first form of the mirrorcoating, in view of the fact that it relies upon a relatively softmaterial, such as copper, is best suited for interior applications, suchas the interior rearview mirror of an automotive vehicle or the like.

EXAMPLE 2

The mirror coating of this example is best understood by a study of FIG.10 and FIG. 11, respectively. In this regard, the mirror coating of thepresent example is generally indicated by the numeral 120, and has afirst layer 121 of silicon having a thickness dimension of 104.98nanometers; a second layer 122 of silicon dioxide having a thicknessdimension of about 39.12 nanometers; a third layer 123 of silicon havinga thickness dimension of about 122.49 nanometers; a fourth layer 124 ofsilicon dioxide having a thickness dimension of about 77.25 nanometers;a fifth layer 125 of silicon having a thickness dimension of about 6.40nanometers; a sixth layer 126 of silicon dioxide having a thicknessdimension of about 69.18 nanometers; a seventh layer 127 of siliconhaving a thickness dimension of about 79.92 nanometers; and an eighthlayer 128 of silicon dioxide having a thickness dimension of about 55.70nanometers.

The second example of the invention is best understood by a study ofFIG. 10 where the mirror coating composition discussed above achieves aluminous reflectance of approximately 50.88% and further, has 1931 CIE xand y color coordinates of approximately 0.3313 and 0.3324 whenilluminated by white light. It should be understood that a substantiallyneutral mirror has 1931 CIE color x and y coordinates of 0.3333 and0.3333, respectively. Similarly the individual layers may vary inthickness by as much as 2% and the specific stoichiometry of thedeposited layers may vary slightly depending upon the depositionprocess. This was discussed with respect to Example 1, above. Further,the peak absorbance, transmittance and reflectance are set forth at anangle of incidence of approximately 30 degrees. As will be recognized,the present example achieves a peak transmittance in excess of 70%; anabsorbance of greater than 30% out-of-band; and a luminous reflectanceof greater than 50%.

EXAMPLE 3

The mirror coating of this example is best understood by a study of FIG.6 and wherein the mirror coating is a non-periodic stack or successionof materials which includes: a first layer of silicon having a thicknessdimension of about 109.12 nanometers; a second layer of silicon dioxidehaving a thickness dimension of about 46.45 nanometers; a third layer ofsilicon having a thickness dimension of about 115.32 nanometers; afourth layer of silicon dioxide having a thickness dimension of about30.25 nanometers; a fifth layer of silicon having a thickness dimensionof about 77.52 nanometers; and a sixth layer of silicon dioxide having athickness dimension of about 131.33 nanometers. It should be understoodthat the present graphical depiction was taken at approximately a 30degree angle of incidence [AOI] and further, this composition achieves aluminous reflectance of about 52.93%. The third form of the mirrorcoating further has a substantially neutral reflected chromaticityhaving 1931 CIE x and y color coordinates of 0.3298 and 0.3222, whenilluminated by white light. It being understood that a substantiallyneutral mirror has an average CIE x and y color coordinates of 0.3333and 0.3333, respectively. As earlier discussed, the thickness of theindividual layers may vary by as much as 2% and the earlier mentionedperformance characteristics which may vary as a consequence ofstoichiometric consideration applies equally to the present example and,therefore, for purposes of brevity, are not repeated herein.

EXAMPLE 4

The mirror coating of the present example is best understood by a studyof FIG. 9, and wherein the mirror coating includes a first layer offerric oxide having a thickness dimension of about 145.30 nanometers; asecond layer of silicon dioxide having a thickness dimension of about72.89 nanometers; a third layer of ferric oxide having a thicknessdimension of about 54.14 nanometers; a fourth layer of silicon dioxidehaving a thickness dimension of about 43.74 nanometers; a fifth layer offerric oxide having a thickness dimension of about 26.0 nanometers; asixth layer of silicon dioxide having a thickness dimension of about133.60 nanometers; and a seventh layer of ferric oxide having athickness dimension of about 85.79 nanometers. The graphic illustrationof the present mirror coating was taken from an angle of incidence [AOI]of approximately 30 degrees. In the example noted above, the mirrorcoating achieves a luminous reflectance of about 50.76%, and further, issubstantially neutral, that is, the mirror coating has a 1931 CIE x andy color coordinates of approximately 0.3566 and 0.3506, respectively,when illuminated by white light. It should be understood that asubstantially neutral mirror has 1931 CIE x and y color coordinates of0.3333 and 0.3333, respectively. As will be recognized, peaktransmittance exceeds 70% within the predetermined band and peakabsorbance is substantially greater than 30% out-of-band. As in theother examples the thickness dimension of the individual layers may bevaried by as much as 2% and the stoichiometry of the individual layersmay effect the individual thicknesses as discussed earlier. In addition,this coating is particularly strong and hard and therefore may be wellsuited for exterior mirror applications.

EXAMPLE 5

The fifth example of the mirror coating is best understood by a study ofFIG. 8, and wherein the mirror coating is a non-periodic stack orsequence of materials which includes: a first layer of ferric oxidehaving a thickness dimension of about 153.81 nanometers; a second layerof silicon dioxide having a thickness dimension of about 60.73nanometers; a third layer of ferric oxide having a thickness dimensionof about 56.13 nanometers; a fourth layer of silicon dioxide having athickness dimension of about 37.96 nanometers; a fifth layer of ferricoxide having a thickness dimension of about 35.61 nanometers; a sixthlayer of silicon dioxide having a thickness dimension of about 131.71nanometers; a seventh layer of ferric oxide having a thickness dimensionof about 89.84 nanometers; and an eighth layer of silicon dioxide havinga thickness dimension of about 144.84 nanometers. The example of thepresent invention, noted above, is graphically illustrated in FIG. 4with respect to a 30 degree angle of incidence [AOI]. Further, thiscoating achieves a luminous reflectance of 51.11%, has a peaktransmittance greater than 70%, and a peak out-of-band absorbancegreater than 30%. Additionally, the mirror coating causes the mirror tobe substantially neutrally chromatic, that is, the fifth example has1931 CIE x and y color coordinates of approximately 0.3400 and 0.3442,respectively, when illuminated by white light. As earlier discussed, asubstantially neutral mirror has 1931 CIE x and y color coordinates of0.3333 and 0.3333, respectively. As in the other examples, this mirrorcoating may also have layers which vary in thickness by as much as 2%and have other stoichiometric variations as discussed earlier.

OPERATION

The operation of the present invention is believed to be readilyapparent and is briefly summarized at this point. As best understood bya study of FIGS. 2, 3 and 6 through 11, a mirror assembly 10 forreflecting light forming a perceivable image into the line of sight ofan observer [not shown] and further, for emitting or receivingelectromagnetic radiation which forms various signals includes, anenclosure or housing 20 defining an aperture 23 and wherein, anassembly, herein shown, as a receiving and/or transmitting device and/orsensor of electromagnetic radiation 30, is borne by the enclosure, andis operable to emit or receive signals formed of electromagneticradiation within a predetermined spectral band or region. The mirrorassembly 10 further includes a mirror 110, which is borne by theenclosure, and which is positioned in the aperture. The mirror 110 iscoated with a mirror coating which exhibits substantially neutralreflected chromaticity as observed with reflected ambient natural light,has a peak transmission of not less than 60% for the electromagneticradiation within a predetermined band pass spectral region, and has apeak absorbance not less than 30% for electromagnetic radiation which iswithin a selected spectral region other than the predetermined spectralband pass region.

As will be recognized by a study of FIGS. 6 through 9, the luminousreflectance for each of the mirror coating examples provided exceed 50%while simultaneously maintaining a peak transmission in thepredetermined spectral band of light, which includes 630-680 nanometersin excess of 70%.

In summary, therefore, it will be seen from the disclosure above, thatthe mirror coatings of the present invention provide a fully dependableand practical means by which a mirror assembly 10 can be assembled andwhich includes a mirror 110 having substantially neutral reflectedchromaticity, as observed with reflected ambient light, has a peaktransmittance not less than 60% within a predetermined spectral bandpass region, has a peak absorbance not less than 30% within a spectralregion other than the predetermined spectral band pass region, and whichsimultaneously has a luminous reflectance greater than 50% for theambient light striking the mirror coating. In addition to the foregoing,the improved mirror coating of the present invention is non-periodic,and further exhibits substantial insensitivity to spectralcharacteristic variations attributable to angle of incidence variationswithin a broad range of useful angles.

It should be apparent to those skilled in the art that the foregoingexamples of the invention have been made for the purposes ofillustration and that variations of the usual magnitude may be made inproportions, procedures and material without departing from the scope ofthe present invention. Therefore, it is intended that this invention notbe limited except by way of the claims which follow.

Having described my new invention what I claim as new and desire tosecure by Letters Patent of the United States is:
 1. A mirror coatingcomprising a recurring succession of two materials which haveindividually variable thicknesses, and which form a layered interferencefilter structure, and wherein the mirror coating exhibits substantiallyneutral reflected chromaticity as observed with reflected visible light,has a peak transmittance of not less than 60% within a predeterminedspectral band pass region, has a peak absorbance of not less than 30%within a spectral region other than the predetermined spectral band passregion, and which simultaneously has a luminous reflectance greater than50% for the visible light striking the mirror coating, and wherein therecurring succession of materials comprises:a first layer of ferricoxide having a thickness dimension of about 145.30 nanometers; a secondlayer of silicon dioxide having a thickness dimension of about 72.89nanometers; a third layer of ferric oxide having a thickness dimensionof about 54.14 nanometers; a fourth layer of silicon dioxide having athickness dimension of about 43.74 nanometers; a fifth layer of ferricoxide having a thickness dimension of about 26.0 nanometers; a sixthlayer of silicon dioxide having a thickness dimension of about 133.60nanometers; and a seventh layer of ferric oxide having a thicknessdimension of about 85.79 nanometers.
 2. A mirror composition as claimedin claim 1, and wherein the thickness dimension of the individual layersmay vary by about 2% or less.
 3. A mirror coating comprising a recurringsuccession of two materials which have individually variablethicknesses, and which form a layered interference filter structure, andwherein the mirror coating exhibits substantially neutral reflectedchromaticity as observed with reflected visible light, has a peaktransmittance of not less than 60% within a predetermined spectral bandpass region, has a peak absorbance of not less than 30% within aspectral region other than the predetermined spectral band pass region,and which simultaneously has a luminous reflectance of greater than 50%for the visible light striking the mirror coating, and wherein therecurring succession of materials comprises:a first layer of ferricoxide having a thickness dimension of about 153.81 nanometers; a secondlayer of silicon oxide having a thickness dimension of about 60.73nanometers; a third layer of ferric oxide having a thickness dimensionof about 56.13 nanometers; a fourth layer of silicon dioxide having athickness dimension of about 37.96 nanometers; a fifth layer of ferricoxide having a thickness dimension of about 35.61 nanometers; a sixthlayer of silicon dioxide having a thickness dimension of about 131.71nanometers; a seventh layer of ferric oxide having a thickness dimensionof about 89.84 nanometers; and an eighth layer of silicon dioxide havinga thickness dimension of about 144.84 nanometers.
 4. A mirrorcomposition as claimed in claim 3, and wherein the thickness dimensionof the individual layers may vary by about 2% or less.